Constructing views in the view architecture

The call on the first phase constructor method of the view occurs in UI controller. The view serves as the top-level window under the UI controller.

The following are the methods that you need to derive for the view derived from CCoeControl :

• Default constructor, which cannot contain code that leaves. A common implementation is:

  
  CMyAppView* CMyAppView::NewL( const TRect& aRect )
      {
      CMyAppView* self = CMyAppView::NewLC( aRect );
      CleanupStack::Pop( self );
      return self;
      }
  
  CMyAppView* CMyAppView::NewLC( const TRect& aRect )
      {
      CMyAppView* self = new ( ELeave ) CMyAppView;
      CleanupStack::PushL( self );
      self->ConstructL( aRect );
      return self;
      }
  
  CMyAppView::CMyAppView()
      {
      // No implementation required
      }

  The declarations for CMyAppView::NewL() and CMyAppView::NewLC() in the class header file needs to be public to support the construction method required.

  In this approach, CMyAppView::NewL() is called from the UI controller. It creates a view object by calling CMyAppView::NewLC() to create the object (and leave if it cannot), pushes a pointer to the clean-up stack in case the second phase construction method leaves, and then calls the second phase construction method of the object. When it returns to CMyAppView::NewL(), the pointer pushed to the cleanup stack is removed.

• Symbian second phase constructor with code that might leave. A common implementation is:

  
  void CMyAppView::ConstructL( const TRect& aRect )
      {
      // Create a window for this application view
      CreateWindowL();
  
       //add construction for other controls if required
  
  	   // Set the windows size
      SetRect( aRect );
  
      // Activate the window, which makes it ready to be drawn
      ActivateL();
      }

  CMyAppView is a private class providing the second phase construction that accepts the rectangle the view is drawn to.

  CCoeControl::CreateWindowL() creates a window for the control. Note that this window is a child of the UI controller. This method makes the control a window-owning control. While, the use of window-owning controls is discouraged to prevent the taxing of run-time resources, this is the top-level window for the UI controller.

  While this is a simple control that does not contain other controls, other controls could be added to the control between CCoeControl::CreateWindowL() and CCoeControl::SetRect(aRect). For more information, see Compound controls in the view architecture.

  CCoeControl::SetRect(aRect) sets the window size according to the requirements of the mobile device. The top-level control rectangle is set to the area that the framework provides for the application. Calling CCoeControl::SetRect(aRect) calls the CCoeControl::SizeChanged() method, where the control should set the position and size for any child controls and thus adjust the control layout to the UI.

  CCoeControl::ActivateL() sets the control as ready to be drawn.

If required for your application, you may need to implement other methods for your control. For top-level windows, you would need to implement CCoeControl::SizeChanged() to respond to changes to the size and position of the contents of this control. This is called by the Symbian platform when a change occurs. A typical implementation for a compound control is:

void CMyAppView::SizeChanged()
    {
    // Control resize code
    iControl->SetExtent( const TPoint &aPosition, const TSize &aSize);
    }